Electric system for controlling motions



April 1943- M. LATTMANN 2,440,147

ELECTRIC SYSTEM'FOR CONTROLLING MOTIONS Filed July 18, 1946 2 Sheets-Sheet 1 l 28 A V 27 E? +3 1. 1o 14 29 11 5 12 l fig. 1

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C g ATYOK/YEYS April 20, 1948. M. LATTMANN ELECTRIC SYSTEM FOR CONTROLLING MOTIONS Filed July 18, 1946 2 Shee ts-Sheet 2 55% fig Avwrm: filw Patented Apr. 20, 1948 UNITED STATES PATENT OFFICE ELECTRIC SYSTEM FOR CONTROLLING MOTIONS Max Lattmann, Zurich, Switzerland Section 1, Public Law 690, August 8, 1946 1 Claim. 1

The present invention relates to systems for controlling motions and in particular for re tering and reproducing motions with the aid of an equipment for magnetic recording of electrical signals.

The method of generating a motion, in particular a rotary motion with a determined time lag relative to an original motion, with the aid of a magnetic recording and reproducing equipment is already known. It consists in transmitting direct current impulses to the movable steel ribbon. The greater the velocity of the original motion, the closer these impulses follow one another. At high velocity it may happen that single impulses are lost in the magnetic recording and reproducing equipment, with the result that the retarded motion no longer corresponds to the original motion. The present invention aims at creating an arrangement in which such errors in the retarded reproduction of an original motion cannot possibly occur.

In a specific preferred embodiment the invention comprises an electric fo1low-up control system in which the velocity of an output member depends on the lag between the controlling motion and the follow-up motion. and in which the latter is generated by a synchronous motor to which is fed a three-phase current of variable frequency. This three-phase current is generated. with the aid of a modulating device in which a three-phase current of constant frequency is modulated with a monophase current whose frequency is proportional to the lag between the controlling motion and the follow-up motion. Electric follow up control systems of this kind are already known. For the purpose of generating a second follow-up motion Whose temporal course tallies exactly with that of the first follow-up motion but is retarded relatively to the latter by a time which may be chosen at will. this embodiment of the invention comprises a second synchronous motor and a device for recording and reproducing alternating currents by means of a magnetizable carrier. Like the first this second synchronous motor is fed by a three-phase current of variable frequency generated in a modulating device by the modulation of a threephase current of constant frequency with a monophase current of variable frequency. This monophase current is generated by the above-mentioned recording and reproducing equipment.

Here a monophase current is recorded on a magnetizable carrier by means of a recording head to which is fed the monophase current utilized in the follow-up control system. This recording induces in a reproducing head, placed at a certain point (which may be chosen at will) of the carrier the monophase current intended for feeding the modulating device of the second synchronous motor.

The nature of the invention will be more fully understood from the following detailed description and by reference to the accompanying drawing of which Fig. l is a general diagram of an arrangement according to the invention;

Fig. 2 shows in detail the circuit H in Fig. 1;

Fig. 3 shows modulating devices l8 and 26 in Fig. 1;

Fig. 4 shows a part of the arrangement in Fig. 1 in an altered form.

The original motion is described by shaft [0 of differential condenser A. This comprises plate l 1 attached to shaft l0 and the pair of plates l2, l3 attached. to shaft M, which plates abut on each other forming a gap. Plate l I and the pair of plates I2, is form part of two concentric, cylindric surfaces. Differential condenser A is fed by transformer i5 connected with a source of alternating current, and whose secondary winding is connected with the pair of plates l2, l3. When plate I! is in a position symmetrical with both plates l2, l3, there is no voltage between plate II and the middle of the secondary winding of transformer 15. On the other hand a voltage is generated as soon as plate H is moved from this position in either direction, Which can be brought about by the rotation of shaft it or of shaft Hi.

The voltage thus produced is fed via leads IE to a circuit 41 that acts as a source of alternating current whose frequency can be increased or decreased relatively to a mean frequency f by means of the voltage generated in differential condenser A. This frequency is increased or decreased accordin to the sense of the relative displacement of the plates of condenser A and the magnitude of the variation Af depends on the magnitude of this displacement. The alternat ing voltage produced in circuit I! is fed on the one side to modulating device I8 of a first followup equipment B and to recording head is of a magnetic recording and reproducing equipment C on the other. The endless steel ribbon 23 of the latter is advanced with uniform speed by means of drums 2i, and driving members not shown in the drawing. On this ribbon is continual-ly recorded the alternating current fed to recording head #9. After a certain time the recording induces in the winding of reproducing head 23 an alternating current of exactly the same frequency as that generated by circuit IT. This alternating voltage is fed to the modulating device 25 of a second follow-up equipment D. By erasing head 2 connected to the battery 25 all recordings on steel ribbon 2B are cancelled before the relative points of the ribbon again reach recording head it.

In each of the two identical follow-up equipments B, D besides the modulating device it, 26 there is a three-phase synchronous motor 2'5. 28. The rotor of motor 2'! is connected with shaft i i of differential condenser A, whereas 1'0- tor 28 via shaft 29 drives the member to which should be transmitted the retarded follow-up mo' tion. Each of the modulating devices i8, 26 is fed via common three-phase line 3i. by a source of alternating current whose frequency is the same as the mean frequency produced by circuit l'i. Furthermore, each of the modulating devices is connected via a three-phase line 32, 83

, with the windings of the rotor of the appurtenant motor 27, 28.

Fig. 2 shows one embodiment of the circuit ll of Fig. 1. It will be seen that there are two repeating coils 3t, 3'! whose secondary windings are each connected to a pair of terminals of a ring modulator 38. The primary winding of repeating coil 33 is connected with leads it of mg. 1, whereas the primary winding of repeating coil 37 is connected with a source of aiternating current of the same frequency as that fed to the primary Winding oftransformer is of Fig. i, The middle of the secondary windings of both repeating coils 3%, ti! is connected with the input termi nals of a filter circuit 39 composed of two shunt condensers 49 and a series coil ti and intended to suppress harmonics generated in the modulator 38. Resistance 32 is connected to the output terminals of filter circuit 39 and forms part of the grid circuit of amplifier tube 43 whose an ode circuit comprises one winding #4 of a repeating coil as and resistance it. The direct current coming from amplifier tube 33 serves to pre-magnetize repeating coil 45. Winding t6 and condenser ll form an oscillatory circuit connected with the grid of tube 48. In addition to repeating coil A9 shunted by the plate resistance the anode circuit of this tube comprises reactance winding 5c of repeating coil 45 and a series re.- sistance 52. The plates of both tubes 53, 43 receive a positive voltage from lead 53 connected to the positive pole of a battery not shown in Fig. 2.

When there is no voltage in the primary winding of repeating coil 36, and this is the case when there is no displacement in condenser A, no current fiows through resistance 42 owing to the symmetry of the circuit. This situation is altered as soon as a displacement occurs in condenser A, since as a result of the voltage applied to transformer !5 (see Fig. 1) in the secondary winding of repeating coil 36 a. current is generated which is in phase or in phase opposition to the current generated by the voltage applied to the primary winding of repeating coil 3? according to whether the displacement in condenser A took place in one direction or the other. As a result of these currents modulation products mak their appearance in modulator circuit 38. The only one of these to reach resistance 42 is that which corresponds to the difference between the two alternating voltages acting on modulator circuit 38 and as in the case in point the frequencies are the same, which forms a direct current. Its direction depends on whether the phases of the two voltages applied to the primary windings of repeating coils 36 and 3! are the same or opposed. In order to fix the steady plate current a constant direct auxiliary voltage not shown in Fi 3 is applied to the grid of the tube 43. When there is a displacement in condenser A, to this auxiliary voltage is added the voltage drop in resistance 42, so that a. displacement in one direction or the other results in an increase or decrease of the plate current relative to the steady plate current. When there is no displacement in condenser A the steady plate current flowing through tube 43 determines the premagnetization of repeating coil 45 and thus defines the mean value 1 of the frequency Produced by tube 48. Any variation of the direct current that flows through winding 44 causes an increase or decrease A) of this frequency J dependent on the magnitude of the displacement in condenser A.

Fig. 3 shows modulating devices l8 and 26 of Fig. 1. Here the alternating current of frequency (ficf) arriving by leads 55 from repeating coil :9 of Fig. 3 is fed in parallel to the primary windings of three repeating coils 56, 51 and 58. Each of these repeating coils forms together with a further repeating coil 59, 69, 6i and a rectifier circuit 62, 63, 64 a modulating device composed in the same manner as shown in Fig. 3. To each of the repeating coils 59, 60, 6| is connected one phase of a three-phase current of frequency f. The primary windings of these repeating coils are connected in star connection to three-phase line 65, whereas their secondary windings as well as those of the repeating coils 56, 51, 5,8 are each connected with two terminals of one of the rec.- tifier circuits 82, 63, as. A derivation is made from the middle points of the secondary windings of both repeating coils of each modulating device and conducted to a. filter circuit composed of an induction coil placed in series and two shunt condensers. These filter circuits do not permit of the passage of any frequency greater than the difference between the modulating frequency fin) and the mean frequency 1. The low-frequency alternating currents present at the output terminals of the three filter circuits 56, El, 68 are led preferably over amplifiers not shown in Fig. 3 and via three phase line 32 or 33 of Fig. 1 to one of the windings of three-phase synchronous motor 2! or 28 of Fig. 1. These motors can advantageously take the form of synchronous reaction type motors which operate Without direct current excitation and whose rotating parts can therefore be constructed with a very small moment of inertia.

The arrangement described above operates as follows: 7

If when shaft ii is at rest shaft Hi occupies a position in which plate i! is symmetrical with plates l2, l3, there is at the output terminals of circuit H in alternating voltage whose frequency is equal to the frequency of, the Source of alternating current that feeds line 3!. This alter.- nating voltage is led direct to modulating device it! and via recording and reproducing equipment C to modulating device 26. In both of these modulating devices it modulates each phase of the three-phase current arriving via line 35. Filter circuits 65, 61, 58 of Fig. 4 allow the pasa e to motors 2i and 28 only of tho e products of modulation that correspond to the ci aret e between the frequencies of the output voltn of circuit H and of the three-phase current led to line 3|. As these frequencies are equal, the rotor windings of both motors receive a direct current. Therefore both motors remain at rest.

When shaft I is displaced from this position of symmetry, at the output terminals of circuit II a voltage appears whose frequency is increased or decreased relatively to the mean frequency f by A). As a result of this at the output terminals of modulating device l8 a three-phase current of frequency (A1) is generated, which sets in motion motor 27 with a speed corresponding to this frequency. The direction of rotation is chosen such that shaft 14 is rotated in the same sense as shaft I 0, viz., shaft l4 follows shaft in. In modulating device 26 the variation of frequency of the output voltage of circuit I! only makes itself felt with a delay determined by the speed of steel ribbon 20 and the distance between recording head l9 and reproducing head 23. After this delay motor 28 also starts revolving and its motion is exactly equal to that of motor 21 but with the above mentioned time lag. If it is desired to vary the time lag between the motions of motors 21 and 28, this is best achieved by varying the distance between recording and reproducing heads lil and 23. If, for instance, reproducing head 23 is displaced, this causes a variation of this voltage induced in it, since during this displacement the speed of steel ribbon 20 relative to recording head I9 differs from that relative to reproducing head 23. As a result of this the motion of motor 28 would no longer be a true reproduction of the motion of motor 21. In the following it will be explained how the error arising from the displacement of one or the other of heads I9, 23 may be eliminated.

Fig. 4 only shows the rotor of the synchronous motor 28 and the reproducing head 23 of the arrangement illustrated in Fig. 1. For the purpose of displacing reproducing head 23 along the recording ribbon screw spindle Ill is provided which terminates in hand crank H and engages in an aperture 12 in reproducing head 23. Screw spindle is also connected mechanically via the two conical gears 13, 14 and shaft 75 with differential gear 16, from which latter a second shaft 11 is fixed to the rotor of synchronous motor 28, while a third shaft 78 is fixed to the member to be driven. From Fig. 2 it is obvious that when reproducing head 23 undergoes no displacement shaft 75 also remains at rest, so that the motion of motor 28 is transmitted, as in the arrange ment illustrated in Fig. 1, direct to shaft 18. When screw spindle 10 is actioned by hand crank H reproducing head 23 is displaced in one direction or the other and shaft 18 receives an additional drive. By suitably choosing the ratio of differential gear 16 and the pitch of screw ill the increase or decrease of the angular velocity of shaft 78 caused by the action of differential gear 16 via shaft 75 is made equal in magnitude and opposite in sign to the increase or decrease caused by the displacement of reproducing head 23. Should it be desired to displace the recording head instead of the reproducing head, the error thus caused in the follow-up of synchronous motor 28 can be eliminated by transmitting an additional motion to synchronous motor 21 in a manner similar to that just described.

In the example described above purely mechanical means were provided for compensating the error caused by the displacement of the reproducing head. The following is an explanation of how the arrangement in Fig. 1 can be altered in order to introduce electrical compensation of the error. For this purpose the magnetic recording and reproducing equipment is provided with three additional sets of recording and reproducing heads. The three additional reproducing heads, are mechanically connected with reproducing head 23 in such a way that all four always undergo the same displacement. Furthermore, modulating device 26 is no longer fed direct by three-phase line 3!, but is connected with the windings of the three additional reproducing heads while line 31 feeds the windings of the additional recording heads. In consequence of this, when the time lag is varied, not only the frequency of the voltage induced in the winding of reproducing head 23 is altered, but also the frequency of the three-phase alternating voltage that feeds modulating device 23, so that the above-mentioned error in the follow-up of motor 28 is likewise eliminated.

What is claimed is:

In a system for controlling follow-up movements in combination a device comprising two parts displaceable with respect to each other of which a first part is primarily moved While the second part moves in accordance with a first follow-up movement; a first driving means comprising a polyphase synchronous motor driving said second part and an electric modulating device. in which each phase of a polyphase current of constant frequency is modulated by a. monophase current of variable frequency, the poly phase current generated in the modulating device being fed to said synchronous motor; an electric oscillatory circuit generating a monophase current whose frequency depends on the relative displacement of the two said parts; a second driving means, comprising a polyphase synchronous motor generating a second fo1low-up movement and an electric modulating device in which each phase of a polyphase current of constant frequency is modulated by a: monophase current of variable frequency; a magnetic recording and reproducing system, comprising a carrier moved with constant speed, a recording head to which is fed said monophase current of variable frequency feeding also the modulating device of said first driving means and a reproducing head, which is connected to the modulating device of said second driving means, the temporal course of said two follow-up movements being the same, the second movement being however delayed by a fixed time with respect to the first movement.

MAX LATTMANN. 

